Method and system to reduce outgassing in a reaction chamber

ABSTRACT

Systems and methods of reducing outgassing of a substance within a reaction chamber of a reactor are disclosed. Exemplary methods include depositing a barrier layer within the reaction chamber and using a scavenging precursor to react with species on a surface of the reaction chamber. Exemplary systems include gas-phase deposition systems, such as atomic layer deposition systems, which include a barrier layer source and/or a scavenging precursor source fluidly coupled to a reaction chamber of the system.

CROSS-REFERENCE TO RELATED APPLICATIONS

This Divisional Application claims priority to U.S. patent application Ser. No. 13/941,134, entitled “METHOD AND SYSTEM TO REDUCE OUTGASSING IN A REACTION CHAMBER,” and filed Jul. 12, 2013, which is incorporated by reference herein.

FIELD OF INVENTION

The present disclosure generally relates to gas-phase reaction methods and systems. More particularly, the disclosure relates to methods and systems to reduce outgassing of materials in a gas-phase reaction chamber.

BACKGROUND OF THE DISCLOSURE

Electronic devices, such as semiconductor devices, and photonic devices, such as light emitting and solar devices, are often formed by, among other things, depositing thin films of materials onto a substrate. Techniques for depositing films include atomic layer deposition (ALD). ALD may be desirable for various applications, because ALD processes are self-limiting, allowing precise, conformal deposition of material onto a substrate.

Atomic layer deposition typically includes gas-phase deposition of a film using two or more precursors, wherein one or more of the precursors may be activated, using, for example, a direct or remote plasma. A typical ALD process includes deposition using two precursors. In this case, a sequence often includes exposing a surface of a substrate to a first precursor to react with species on the surface of the substrate in a reaction chamber, purging the reaction chamber to remove the first precursor, exposing the surface of the substrate to a second precursor to react with species from the first precursor in the reaction chamber, and removing the second precursor from the reaction chamber. If each precursor is not sufficiently purged prior to the introduction of the other precursor into the reaction chamber, undesired gas-phase reactions may occur, which may, in turn, cause undesired particle formation or non-uniformity of the deposited film. Additionally or alternatively, insufficient purging of a precursor can result in depletion of a subsequently-introduced precursor.

During an ALD deposition process, one or more of the precursors may adsorb onto or be absorbed into a film formed on a surface of the reaction chamber and subsequently outgas during a cycle in which the other precursor is introduced into the reaction chamber. In this case, undesired gas-phase reactions may occur as one precursor outgasses as the other flows through the reaction chamber.

By way of example, when ALD is used to form a metal oxide film on a surface of a substrate, a method to form the metal oxide film may include exposing the substrate surface to a metal-containing precursor to react with chemical species on the substrate surface, purging the reaction chamber, exposing the substrate surface to an oxidant, such as oxygen, activated oxygen, ozone, water, or alcohol, and then purging the reaction chamber. These steps are repeated until a desired amount of the metal oxide is formed on the surface of the substrate. During these steps, the metal oxide film material is also deposited onto surfaces on the reaction chamber—in addition to the substrate surface. If the oxidant is absorbed into or adsorbed onto the material deposited onto the surface of a reaction chamber, the oxidant may not be completely purged from the reaction chamber during a purge step, and may therefore outgas during a subsequent step of exposing the substrate surface to a metal-containing precursor. As the oxidant outgasses, it may react with the metal-containing precursor during the step of exposing the substrate surface to a metal-containing precursor, resulting in undesired non-uniformity of the film across the substrate surface and/or particle formation within the reaction chamber.

To mitigate the outgassing of a precursor, the ALD process may be run at a relatively low pressure—e.g., less than 0.01 Torr—to enhance purging of the precursors. However, reducing the operating pressure of the reaction chamber to such low pressures generally decreases the throughput of the ALD process, and thus systems and methods operating at these pressures are not well suited for production of devices. Accordingly, improved methods and systems for mitigating outgassing from a reaction chamber during gas-phase reactions are desired.

SUMMARY OF THE DISCLOSURE

Various embodiments of the present disclosure relate to methods and systems for mitigating outgassing of substances within a reaction chamber of a reactor. While the ways in which various embodiments of the disclosure address the drawbacks of the prior art methods and systems are discussed in more detail below, in general, the present disclosure provides systems and methods for providing a barrier layer, using a scavenging agent to react with one or more substances that might otherwise outgas, or otherwise blocking a substance within a reaction chamber to thereby mitigate or prevent outgassing of the substance(s) during subsequent processing within the reaction chamber.

In accordance with various embodiments of the disclosure, methods of reducing outgassing of a substance include the steps of providing a gas-phase reactor having a reaction chamber, forming a barrier layer on a surface within the reaction chamber, depositing material onto a surface of a substrate within the reaction chamber, and removing the substrate from the reaction chamber. The barrier layer may include, for example, a transition metal oxide (e.g., TiO₂, Ta₂O₅, HfO₂, or Al₂O₃ or SiO₂), a transition metal nitride (e.g., TiN), a transition metal oxynitride (e.g., TiON), and/or a transition metal carbide (e.g., TiC). A thickness of the barrier layer may vary according to application, and may be greater than one monolayer, greater than two monolayers, or between about one monolayer and about 50 Å, about 5 Å and about 20 Å, or about 10 Å and about 20 Å. In accordance with various aspects of these embodiments, the step of providing a gas-phase reactor comprises providing an atomic layer deposition (ALD) reactor. In accordance with further aspects, the step of depositing includes providing a first precursor to the reaction chamber, the first precursor reacting with a surface of the substrate to form a first surface species, purging the first precursor from the reaction chamber—e.g., using low pressure and/or a carrier gas, providing a second precursor to the reaction chamber to react with the first surface species to form a second surface species, and purging the second precursor from the reaction chamber. The methods may be particularly useful when the material deposited onto the substrate (and onto a surface within a reaction chamber) includes hygroscopic material, such as lanthanum oxide, magnesium oxide, barium oxide, strontium oxide, or other materials that tend to absorb or adsorb one or more of the precursors. Exemplary methods improve thickness uniformity of material deposited onto the substrate, increase a number of runs within the reaction chamber between cleaning cycles, and produce films of higher quality, compared to similar films produced without forming the barrier layer within the reaction chamber.

In accordance with additional embodiments of the disclosure, a system for depositing material onto a substrate and for mitigating outgassing of a substance within a reaction chamber includes a reactor, such as an ALD reactor, including a reaction chamber, a first precursor source fluidly coupled to the reaction chamber, a second precursor source fluidly coupled to the reaction chamber, a purge gas fluidly coupled to the reaction chamber, and a barrier layer precursor fluidly coupled to the reaction chamber. In accordance with exemplary aspects of these embodiments, the system is configured to form a barrier layer on a surface within the reaction chamber after a substrate is removed from the reaction chamber or before the substrate enters the reaction chamber. In accordance with further aspects, the barrier layer precursor may be selected from, for example, one or more of transition metal oxide precursors, transition metal nitride precursors, transition metal oxynitride precursors, transition metal carbide precursors, silicon oxide precursors, and aluminum oxide precursors.

In accordance with additional embodiments of the disclosure, methods of reducing outgassing of a substance within a reaction chamber include the steps of providing a gas-phase reactor having a reaction chamber, depositing material onto a surface of a substrate within the reaction chamber (and onto a surface within the reaction chamber), and providing a scavenging precursor to the reaction chamber to react with the material on a surface of the reaction chamber. In accordance with various aspects of these embodiments, the scavenging gas is or substantially is consumed or depleted prior to reaching the substrate or the substrate holder—e.g., using dose control. The scavenging precursor may be, for example, a metal halide or an organometallic compound, such as hafnium chloride, silicon chloride, zirconium chloride, or TMA. In accordance with exemplary aspects of these embodiments, the step of depositing material onto a surface includes providing a first precursor to the reaction chamber to react with a surface of the substrate to form a first surface species, purging the first precursor from the reaction chamber, providing a second precursor to the reaction chamber to react with the first surface species to form a second surface species and purging the second precursor. In these cases, the step of providing a scavenging precursor may occur after the step of providing a first precursor and/or before the step of purging the first precursor. Alternatively, the step of providing a scavenging precursor may occur after the step of purging the first precursor. A method may also include a step of purging the scavenging precursor—e.g., prior to the step of providing the second precursor. In accordance with various aspects of these embodiments, the methods may include a step of dose front monitoring, which allows tuning of a process to mitigate or prevent the scavenging precursor from reacting with a surface on the substrate. In other words, the method may be tuned to consume all or nearly all of the scavenging precursor upstream of the substrate.

In accordance with additional embodiments of the disclosure, a system for depositing material onto a substrate and for mitigating outgassing of a substance within a reaction chamber includes a reactor, such as an ALD reactor, including a reaction chamber, a first precursor source fluidly coupled to the reaction chamber, a second precursor source fluidly coupled to the reaction chamber, a purge gas fluidly coupled to the reaction chamber, and a scavenging precursor source fluidly coupled to the reaction chamber. In accordance with exemplary aspects of these embodiments, the reaction chamber is exposed to a first precursor, and after the reaction chamber is exposed to the first precursor, the reaction chamber is exposed to a scavenging precursor, and after the reaction chamber is exposed to the scavenging precursor, the reaction chamber is exposed to a second precursor. Systems in accordance with these embodiments may include dose front monitoring devices, such as one or more quartz crystal microbalances to tune the system, such that all or nearly all of the scavenging precursor is consumed upstream of the substrate.

Both the foregoing summary and the following detailed description are exemplary and explanatory only and are not restrictive of the disclosure or the claimed invention

BRIEF DESCRIPTION OF THE DRAWING FIGURES

A more complete understanding of the embodiments of the present disclosure may be derived by referring to the detailed description and claims when considered in connection with the following illustrative figures.

FIG. 1 illustrates a system for use in accordance with exemplary embodiments of the disclosure;

FIG. 2 illustrates a method for reducing outgassing of a substance in accordance with exemplary embodiments of the disclosure;

FIG. 3 illustrates another system in accordance with exemplary embodiments of the disclosure;

FIG. 4 illustrates a portion of a reaction chamber in accordance with exemplary embodiments of the disclosure;

FIG. 5 illustrates another portion of a reaction chamber in accordance with further exemplary embodiments of the disclosure;

FIG. 6 illustrates another method for reducing outgassing of a substance in accordance with yet additional exemplary embodiments of the disclosure;

FIG. 7 illustrates a process in accordance with yet further exemplary embodiments of the disclosure; and

FIG. 8 illustrates another process in accordance with additional exemplary embodiments of the disclosure.

It will be appreciated that elements in the figures are illustrated for simplicity and clarity and have not necessarily been drawn to scale. For example, the dimensions of some of the elements in the figures may be exaggerated relative to other elements to help to improve the understanding of illustrated embodiments of the present disclosure.

DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS OF THE DISCLOSURE

The description of exemplary embodiments of methods and systems provided below is merely exemplary and is intended for purposes of illustration only; the following description is not intended to limit the scope of the disclosure or the claims. Moreover, recitation of multiple embodiments having stated features is not intended to exclude other embodiments having additional features or other embodiments incorporating different combinations of the stated features.

The present disclosure generally relates to gas-phase reactors, systems and methods. More particularly, the disclosure relates to reactors, systems, and methods that mitigate outgassing of substances from an interior surface of a reaction chamber—e.g., mitigate outgassing from material deposited onto an interior surface of a reaction chamber.

FIG. 1 illustrates a system 100, including a reactor 102. In the illustrated example, system 100 includes a first precursor source 104, a second precursor source 106, a barrier layer precursor source 108, a purge gas source 110, an optional mixer 112, an optional intake plenum 114, and a vacuum source 116. Sources 104-110 may be coupled to mixer 112 or reactor 102 using lines 118-132 and valves 134-140.

Reactor 102 may be a standalone reactor or part of a cluster tool. Further, reactor 102 may be dedicated to a particular process, such as a deposition process, or reactor 102 may be used for other processes—e.g., for layer passivation and/or etch processing. For example, reactor 102 may include a reactor typically used for atomic layer deposition (ALD) processing, such as a Pulsar 3000, available from ASM, and may include direct plasma, and/or remote plasma apparatus. Using a plasma may enhance the reactivity of one or more precursors. By way of one example, reactor 102 includes a reactor suitable for ALD deposition of a dielectric material onto a substrate 142. An exemplary ALD reactor suitable for system 100 is described in United States Patent Application Publication No. US 2012/0266821, the contents of which are hereby incorporated herein by reference, to the extent such contents do not conflict with the present disclosure. An operating pressure of a reaction chamber 144 of reactor 102 may vary in accordance with various factors. Reactor 102 may be configured to operate at near atmospheric pressure or at lower pressures. By way of examples, an operating pressure of reactor 102 during deposition and purge steps range from about 0.01 Torr to about 100 Torr or about 1 Torr to about 5 Torr.

Exemplary first precursors for precursor source 104 include, for example, one or more organometallic compounds or metal halide compounds. By way of examples, precursor source includes one or more compounds selected from the group consisting of hafnium chloride (HfCl₄) and trimethylaluminum (TMA).

Exemplary second precursors for precursor source 106 include oxidants, such as oxygen, activated oxygen, ozone, water, or alcohol. By way of particular examples, precursor source 106 includes water.

Exemplary precursors for barrier layer source 108 may include one or more precursors that react with adsorbed or absorbed material from source 104 and/or source 106 to form a less volatile compound. Suitable precursors for source 108 include transition metal oxide, transition metal nitride, transition metal oxynitride, and transition metal carbide material precursors. By way of examples, precursor source 108 includes a metal halide, such as HfCl₄.

Purge gas source 110 may include any suitable purge or carrier gas. Exemplary gasses include nitrogen, argon, helium, and hydrogen.

System 100 may include a gas distribution system. An exemplary gas distribution system, which allows for fast switching between gasses (e.g., from sources 104-110) is set forth U.S. Pat. No. 8,152,922 to Schmidt et al., issued Apr. 10, 2012, entitled “Gas Mixer and Manifold Assembly for ALD Reactor,” the contents of which are hereby incorporated herein by reference, to the extent the contents do not conflict with the present disclosure. The gas distribution system may be used to, for example, mix a precursor gas and a carrier gas (which may be the same or different from a purge gas from purge gas source 108) prior to the gasses reaching plenum 114 or reactor 102. Further, although illustrated with a horizontal flow across substrate 142 (in the direction of the arrows in FIG. 1) reactors in accordance with alternative embodiments may include a vertical flow, for example, flow emanating from a showerhead and flowing substantially downward onto a substrate.

An exemplary ALD deposition process using a system, such as system 100, includes exposing a surface of substrate 142 within reaction chamber 144 of reactor 102 to a first precursor (e.g., an organometallic compound or a metal halide compound from source 104) that reacts with a species on a surface of substrate 142 to form a first surface species, purging the first precursor (e.g., using a purge gas from source 110), exposing the first surface species to a second precursor (e.g., an oxidant, such as water, from source 106) to form a second surface species, and purging the second precursor from the reaction chamber. Alternatively, an exemplary ALD sequences may begin with exposure to an oxidant, followed by a purge, which is followed by exposure to a second precursor, which is followed by a purge. In the system illustrated in FIG. 1, a precursor gas may be mixed with a carrier gas, such as a purge gas from source 110, at mixer 112, and the mixture of the precursor and the carrier can be introduced into reaction chamber 144 using plenum 114. The direction of the flow of the precursor and purge gas is generally indicated by the arrows in FIG. 1.

Several films formed using this technique may adsorb or absorb a precursor (e.g., from source 104 or 106) that may then outgas as the film is exposed to the other precursor. For example, a film such as lanthanum oxide, magnesium oxide, barium oxide, and strontium oxide may be hygroscopic. In this case, if water is used as an oxidant, the water may be absorbed by the deposited film and may not adequately be purged during a purge cycle. The water may therefore outgas during a step of exposing a substrate to another precursor. When this undesired outgassing of a precursor occurs as the film is exposed another other precursor, high particle counts and reduced uniformity of film deposited onto the substrate may result.

FIG. 2 illustrates a method 200 of reducing outgassing of a substance. Method 200 includes the steps of providing a gas-phase reactor having a reaction chamber (step 202), forming a barrier layer on a surface of the reaction chamber to mitigate outgassing of one or more gasses (step 204), depositing material onto a surface of a substrate within the reaction chamber (step 206), and removing the substrate from the reaction chamber (step 208). In accordance with exemplary aspects of these embodiments, the method produces films having relatively low particle counts—e.g., less than 10 particles having a size of greater than 32 nm on a 300 mm substrate. Additionally or alternatively, the method produces films having non-uniformity values of less than one percent one sigma.

Step 202 includes providing a gas-phase reactor, such as reactor 102 of system 100. As noted above, the reactor may include an ALD reactor, such as a horizontal flow reactor. The reactor may operate at a pressure of about 0.01 Torr to about 100 Torr or about 1 Torr to about 5 Torr and a temperature of about 100° C. to about 600° C. or about 200° C. to about 350° C.

To mitigate undesired outgassing of a substance, such as a first precursor or a second precursor that may be absorbed by or adsorbed onto material deposited onto an interior surface of a reaction chamber, a barrier layer is deposited onto the wetted surfaces or portions thereof within the reactor during step 204. As used herein, wetted surfaces of the reactor refer to surfaces within the reactor that are exposed to the deposition gasses, such as precursors from sources 104 and 106. Exemplary barrier layers include transition metal oxides, nitrides, oxynitrides, and carbides, as well as silicon oxide and aluminum oxide. By way of particular examples, the barrier layer includes material selected from one or more of TiO₂, TiN, TiON, TiC, Ta₂O₅, HlO₂, SiO₂, and Al₂O₃. In accordance with exemplary aspects of these embodiments, a barrier layer is formed by reacting a precursor (e.g., from source 108) with a species (e.g., an oxidant) to form the barrier layer.

A thickness of a barrier layer deposited during step 204 may vary in accordance with, for example, the material deposited onto a surface of a substrate, a thickness of the material deposited during step 204, a number of substrates processed during step 206, and the like. By way of examples, a thickness of the barrier layer may be greater than one monolayer, greater than two monolayers, or between about one monolayer and about 50 Å, about 5 Å to about 20 Å, or about 10 Å to about 20 Å.

During step 206, material is deposited onto a surface of a substrate, such as substrate 142. The surface of the substrate may have any suitable topography, including planar and/or non-planar surfaces that are exposed for deposition, and the substrate may include layers of various materials, such as materials used to form semiconductor and/or photonic devices. For example, a surface may include a top surface or a portion thereof (including topology) of a semiconductor or photonic device workpiece or wafer. Step 206 may suitably include depositing material using an ALD process. In this case, step 206 may include the substeps of providing a first precursor (e.g., from source 104) to the reaction chamber, the first precursor reacting with a surface of the substrate to form a first surface species, purging the first precursor from the reaction chamber (e.g., using a purge gas from source 110), providing a second precursor (e.g., from source 106) to the reaction chamber to react with the first surface species to form a second surface species, and purging the second precursor from the reaction chamber. These steps may be repeated a desired number of times until a desired or predetermined amount of material is formed on the surface of the substrate.

At step 208, the substrate is removed from the reaction chamber. By way of example, a substrate supported on a substrate support during step 204 can be removed from reaction chamber 144 of reactor 102 by moving the support to an unload position and then removing the substrate from the reactor. Although illustrated as process 200 progressing to step 208, material may be deposited onto multiple substrates, concurrently or sequentially during step 206 and removed from the reactor during step 208. Steps 204-208 may be repeated a desired number of times.

Turning now to FIG. 3, a system 300, in accordance with additional embodiments of the disclosure, is illustrated. System 300 is similar to system 100, except system 300 includes a scavenging precursor source 302 for providing a scavenging precursor to reaction chamber 144 of reactor 102.

Exemplary scavenging precursors suitable for use with exemplary embodiments of the disclosure include metal halides, such as metal chlorides, and organometallic compounds. By way of particular examples, scavenging precursor source 302 includes hafnium chloride or silicon chloride.

Exemplary systems in accordance with various embodiments of the disclosure include one or more dose front monitoring devices to enable tuning of the system. FIG. 4 illustrates a portion 400 of an interior of a reaction chamber, such as chamber 144, which includes a first dose front monitoring device 402 and a second dose front monitoring device 404 located upstream of substrate 142 (or a location where substrate 142 would reside). Exemplary dose front monitoring devices include quartz crystal microbalances.

The dose front monitoring devices may be mounted onto a lower portion 304 of reactor 102 and within reaction chamber 144. The dose front monitoring devices may be used to tune process conditions, such that wetted surfaces of a reaction chamber that are upstream of the substrate can be exposed to the scavenging precursor, and all or nearly all of the scavenging precursor is consumed (e.g., reacts with) a species on the reaction chamber surface prior to reaching substrate 142. For example, the system may be tuned, such that a Stokes front of the scavenging precursor substantially falls to zero upstream of (e.g., near) substrate 142. This allows the scavenging precursor to be used during a deposition process, rather than removing a substrate prior to exposing the reaction chamber to the scavenging precursor.

FIG. 5 illustrates another example of portion 400, in which the dose front monitors are located further apart. In the illustrated case, monitor 404 is located downstream of substrate 142. In this case, additional and/or more complex calculations may be required to tune the reactor, such that all or nearly all of the scavenging precursor is consumed prior to reaching substrate 142.

FIG. 6 illustrates a method 600 of reducing outgassing of a substance within a reaction chamber in accordance with additional exemplary embodiments of the disclosure. Method 600 includes the steps of providing a gas-phase reactor having a reaction chamber (step 602), depositing material onto a surface or a substrate within the reaction chamber (step 604), and providing a scavenging precursor to the reaction chamber to react with the material on a surface of the reaction chamber (step 606).

Providing a gas-phase reactor step 602 may include providing any suitable reactor, such as the reactors disclosed herein. In accordance with various examples, step 602 includes providing an ALD reactor.

During step 604, material may be deposited using, for example, an ALD process. In this case, step 604 may include providing a first precursor to the reaction chamber to react with a surface of the substrate to form a first surface species, purging the first precursor from the reaction chamber, providing a second precursor to the reaction chamber to react with the first surface species to form a second surface species, and purging the second precursor from the reaction chamber.

Although illustrated as separate steps 604, 606, portions of steps 604 and 606 may overlap. FIG. 7 illustrates a process 700, which includes an exemplary combination of steps 604 and 606.

In the illustrated example, process 700 includes providing a first precursor to the reaction chamber to react with a surface of a substrate to form a first surface species (step 702), providing a scavenging precursor to the reaction chamber to react with the material on a surface of the reaction chamber—e.g., upstream of the substrate (step 704), purging the first precursor and the scavenging precursor from the reaction chamber (step 706), providing a second precursor to the reaction chamber to react with the first surface species to form a second surface species (step 708), and purging the second precursor from the reaction chamber (step 710). Step 704 may include providing the scavenging precursor, such that all or nearly all of the scavenging precursor is consumed prior to reaching the substrate. Process 700 may be repeated a desired number of times until a desired thickness of material is formed on a substrate. And, the precursors and purge gasses used for this process may include any of the precursors and purge gases noted herein.

FIG. 8 illustrates another process 800, which includes an alternative exemplary combination of steps 604 and 606. Process 800 is similar to process 700, except process 800 includes an additional purge step 804. Steps 802, 806, 808, 810, and 812 may correspond to steps 702-710, respectively, of process 700, except step 808 may be shorter in duration and/or be at higher pressure, since less precursor material may be removed during this step, compared to step 706.

Although exemplary embodiments of the present disclosure are set forth herein, it should be appreciated that the disclosure is not so limited. For example, although the system and method are described in connection with various specific chemistries, the disclosure is not necessarily limited to these examples. Further, although methods are illustrated in a particular sequence, the method is not limited to such sequence of steps, unless indicated herein to the contrary. Various modifications, variations, and enhancements of the system and method set forth herein may be made without departing from the spirit and scope of the present disclosure.

The subject matter of the present disclosure includes all novel and nonobvious combinations and subcombinations of the various processes, systems and configurations, and other features, functions, acts, and/or properties disclosed herein, as well as any and all equivalents thereof 

1. A method of reducing outgassing of a substance, the method comprising the steps of: providing a gas-phase reactor having a reaction chamber; forming a barrier layer on a surface of the reaction chamber to mitigate outgassing of one or more gasses; depositing material onto a surface of a substrate within the reaction chamber; and removing the substrate from the reaction chamber.
 2. The method of reducing outgassing of a substance of claim 1, wherein the step of providing a gas-phase reactor comprises providing an atomic layer deposition reactor.
 3. The method of reducing outgassing of a substance of claim 1, wherein the step of depositing comprises: providing a first precursor to the reaction chamber, the first precursor reacting with a surface of the substrate to form a first surface species; purging the first precursor from the reaction chamber; providing a second precursor to the reaction chamber to react with the first surface species to form a second surface species; and purging the second precursor from the reaction chamber.
 4. The method of reducing outgassing of a substance of claim 1, wherein the step of forming a barrier layer comprises forming a layer selected from one or more of: a transition metal oxide layer, a transition metal nitride layer, a transition metal oxynitride layer, and a transition metal carbide layer.
 5. The method of reducing outgassing of a substance of claim 1, wherein the step of forming a barrier layer comprises forming a layer comprising one or more of TiO₂, Ta₂O₅, HfO₂, SiO₂, Al₂O₃,TiN, TiON, and TiC.
 6. The method of reducing outgassing of a substance of claim 1, wherein the step of forming a barrier layer comprises forming a layer comprising Al₂O₃.
 7. The method of reducing outgassing of a substance of claim 1, wherein the step of forming a barrier layer comprises depositing between about one monolayer and about 50 Å of barrier material onto the surface of the reaction chamber. 